1. Field
The exemplary embodiments generally relate to substrate transfer systems and, more particularly, to a robot transfer arm of a substrate transport apparatus.
2. Brief Description of Related Developments
The processing of semiconductors often involves multiple process steps that are performed by single step tools. Such processing steps include the photo etching of the film deposited on a substrate, dry stripping, bevel edge processing, as well as heating, cooling and cleaning.
Each of the process operations is generally performed under vacuum in a specialized process chamber. Because of the need for extreme cleanliness and the delicate nature of each process, batch processing of semiconductor substrates has generally been replaced by individual substrate processing. This allows more control of the processing of each substrate, but limits the overall throughput of the system, because, for each process step, the process chamber must be vented, the substrate loaded, the chamber sealed and pumped to vacuum. After processing, the steps are reversed.
To improve the process volume, in a conventional manner a cluster of processing chambers are arranged around a conventional substrate transport chamber which is constructed to be kept under vacuum. One or more load lock chambers are connected through slit valves to the transport chamber, the transport chamber is connected to a front end module and generally multiple load port modules are coupled to the front end unit.
The load locks accommodate cassettes of substrates to be processed. The cassettes are delivered to the load lock by the front end delivery transport located in the front end module of the system. A load lock constructed to accommodate such cassettes is shown in U.S. Pat. No. 5,664,925 owned in common with the subject application. The disclosure of the '925 patent is incorporated herein by reference, in its entirety.
In this manner cycling times are reduced, while significantly increasing system throughput. The process and transport chambers are maintained continuously under vacuum, while only the load lock is cycled. The load lock receives the substrates to be processed after being sealed from the transport chamber and vented to atmosphere. The front end port is then sealed and the load lock is pumped to a vacuum consistent with the transport and processing chambers.
A robotic transfer mechanism is mounted within the transport chamber and operates to remove substrates from the load lock and deliver them to the selected process chambers. After processing, the substrates are picked up by the robot and transported to the next process chamber or to a load lock for removal from the transport chamber. In some instances, for timing purposes, these systems may employ buffer stations which are adapted to store substrates either before loading or at other times during the transport of the substrate through the system.
A system of this type is described in U.S. Pat. No. 5,882,413 and an example of a robotic transfer mechanism is shown in U.S. Pat. No. 5,647,724, each of which is assigned to an owner common to this application. The disclosures of these patents are incorporated herein by reference in their entirety.
It has been found that substrates up to 200 mm in diameter can be effectively processed with the conventional cluster type systems. As can be realized, the size of conventional cluster tools is largely dependent on the size of the conventional transport chamber, with communication to each of the processing modules of the cluster tool. Further, there is a trend towards increasing diameters and the cluster systems become unduly large when processing substrates of 300 mm, 450 mm or more in diameter. Processing systems having transports with two arm links may be used to reduce the containment to extension ratio of the transports. However, as the diameter or size of the substrates increases, the length of each of the two arm links of the transport also increases, thereby increasing the volume to accommodate the arm motion in the transport chamber.
As process device geometries shrink, film thickness reduces, suggesting shorter deposition and removal processing times. The pumping down of larger volume load locks may conflict with the shorter deposition and removal times as the pumping down of the load lock may take longer than the processing times.
It would be advantageous to have a compact substrate transport system allowing for decreased load lock pump down time. It would also be advantageous to have a substrate transport system that allows multiple processing modules to be arranged in close proximity to each other maximizing production facility floor space. It would further be advantageous to have a substrate transport system that can directly couple a load port with a processing module without the use of an equipment front end module.